Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to sizing paper with ketene dimer
sizes under alkaline papermaking conditions.
Use of ketene dimers as sizing agents in papermaking, usually
at alkaline pH levels, is well known. Ketene dimer sizes function
5 by forming covalent bonds with cellulose to give proper orientation
and anchoring of the hydrophobic chains. Ketene dimers and their
hydrolysis products (stearones) are waxy solids that can reduce the
coefficient of friction (COF) of the paper surface, and thus
contribute to slipperiness, particularly when added internally at
10 high levels (greater than 0.lS weight%), or when used as a surface
size.
Reduced COF contributes to problems in paper handling and
converting, including telescoping of paper rolls, as well as
sliding of stacked, flattened cardboard boxes. A low COF can also
15 cause potential conversion problems with fine paper grades, such as
bond and reprographic paper grades.
To help control the COF of alkyl ketene dimer-sized paper, a
solution of colloidal silica has been conventionally applied
directly to the surface of paper sheets and boxes at the end of the
20 manufacturing process. This requires an extra step in the
papermaking process, reducing productivity and increasing costs.
U.S. Patent No. 2,865,743 to C. A. Weisgerber discloses a
process for internal sizing of paper by dispersing a ketene dimer
on a carrier comprising finely-divided amorphous silica to form a
25 free-flowing powder in which the particles of silica have a high
level of oil absorption and contain a deposit or coating of the
ketene dimer. The patent claims that the powder is readily
dispersible without the need for a dispersing agent.
British Patent 804,504 to C. A. Weisgerber discloses a process
30 of sizing paper which comprises the addition of activated clay and
a sizing material which reacts chemically with the hydroxyl groups
of cellulose such as ketene dimers, anhydrides, or organic
isocyanates.
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~ According to the invention, a composition containing a ketene
dimer for sizing paper is characterized in that it is a stable
aquasol of a positively charged colloidal silica, positively
charged colloidal alumina, or positively charged colloidal
zirconia, and also contains the ketene dimer.
Also, according to the invention, a method for sizing a paper
product of sheeted cellulosic fibers comprising treating the
fibers with a ketene dimer size, is characterized in that the
fibers are treated internally or externally with a stable aquasol
of positively charged colloidal silica, positively charged
colloidal alumina, or positively charged colloidal zirconia, that
also contains the ketene dimer.
The composition can be conventionally incorporated internally
by adding it to the paper-making furnish or applied as a surface
size to achieve the desired level of sizing while increasing the
COF.
Also according to the invention, a paper product comprises
sheeted cellulosic fibers treated with the composition or the
process according to the invention.
Stable cationic aquasols of colloidal silica, alumina, and
zirconia are well known, for instance from U.S. Patents 3,007,878,
3,620,978, 3,719,607, 3,754,126 and 3l956,171. Typically, such
sols contain colloidal, dense, finely divided particles, e.g.,
silica, having a surface area of about 20-600 square meters per
gram, about 5-150~m in diameter. They are generally stabilized
with a small amount of an alkali, such as sodium hydroxide.
Typical known aquasols are those containing positively charged
particles having a dense silica core coated with a hydroxyl or
other oxygen compound of a polyvalent metal such as aluminum,
along with an anionic counter ion such as a nitrate ion.
Preferred cationic silica dispersions are available ~rom Nalco
Chemical under the name NALCO*-lSJ612, or from E. I. du Pont de
Nemours & Co. under the name LU~OX*CL. Examples of stable
aquasols of colloidal zirconia suitable for use in the composition
and method according to the invention include zirconia-nitrate
stabilized available under the name NYACOL* Zr-50-20 or Zr-100-20
from Nyacol Products Inc., Ashland, MA, and a suitable example of
stable aquasols of colloidal alumina is a colloidal alumina
dispersion available under the name NYACOL* Al-20 from Nycol
Products Inc.
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~ * Denotes Trade Mark
5 ~ -i
Ketene dimer sizes useful in accordance with the present
invention are well known cellulose-reactive sizing materials. They
include cationic, anionic, and non-ionic materials such as alkyl
(including Cl~~22) and cycloalkyl ketene dimers, aryl and aralkyl
5 ketene dimers, and mixtures thereof. The present invention also
contemplates the use of known stabilizers, such as cationic starch
and cationic polymers, and other adjuvants in conjunction with the
ketene dimer size. Typical ketene dimer sizes as well as
stabilizers and other adjuvants are disclosed in many U.S. Patents,
lo including Nos. 4,240,935, 4,522,686, 4,861,376, 4,919,724, and
4,927,496.
The amount of the ketene dimer applied to paper in accordance
with the present invention will vary conventionally depending on
the type of paper or pulp to be sized, ketene dimer size used, and
15 amount of slzing desired. Preferably, the amount of ketene dimer
applied either internally or as a surface size is about 0.01 to
about 1.0% by weight% based on the dry weight of fiber, more
preferably about 0.05 to about 0.2~ by weight.
The stability criteria for the sol containing the ketene dimer
20 size is that the viscosity value of the material is preferably less
than 100 cps after storage for four weeks at 32~C.
The amount of silica used varies depending on the amount of
ketene dimer employed. Preferably, up to 33 parts by weight of
particulate silica per 100 parts by weight ketene dimer is used.
Optionally, alum is included in the aquasol, preferably at
higher levels of silica, in order to aid in stabilization.
Preferably, the amount of alum varies from 0.1 to 2.5% by weight of
the composition. As an alternative to alum, polyaluminum chloride
can be used in similar amounts. Dispersions of negatively charged
30 colloidal silica, such as available from Du Pont Company under the
designations LUDOX*HS-30 and HS-40, can also be mixed with the
aquasol, with enough cationic material to convert the overall blend
of the colloidal ingredients to a positive charge.
In the following examples, all parts and percentages are by
35 weight unless indicated otherwise.
* Denotes Trade Mark
I ~ _ 4 _
EXAMPLES 1-3
Materials are prepared as follows. A stirred mixture in 92.17
parts water of 1.5 parts cationic starch having an ash content of
3-6%, maximum moisture of 12~, pH 3.5-5.5, 10% maximum common
5 starch, 2.5% amylose maximum, maximum 5% eosin stain, 1.5% minimum
protein, 0.24% minimum nitrogen, and viscosity (cold funnel ratio
1-2.5, 190/75 ~C.) of 45-60 (available under the name AMAIzo~2la7
from American Maize-Products Company, Hammond, IN) and 0.25 parts
sodium lignin sulfonate dispersant (available from Ligno Tech,
10 Greenwich, CT under the name LIGNISOL*XD) is heated at about 95~C
for about 30 minutes at neutral pH. Water lost through evaporation
is replaced, cooling the solution to about 65~C. To the mixture is
added 6 parts of a mixed hexadecyl-hexadecanyl-ketene dimer size,
prepared from a mixture of 45% stearic acid and 55% palmitic acid
15 by forming the acid chlorides thereon and then reacting the acid
chlorides with a tertiary amine and 0.06 parts of a biocide
(Biocide N521 available from Stauffer Chemical) and the mixture is
blended until homogeneous. The resulting pre-mix is homogenized
(about 211 kg/cm2 at 65OC with the collected homogenizate cooled to
20 about 21~C in a cold water bath). Alum (0.02 parts) is then added.
The size is available from Hercules Incorporated under the name
Aquapel 360XC (U.S. Patent 4,927,496).
To the foregoing mixture, which is kept under stirring in a
container at room temperature (about 25~C), a cationic silica sol
25 dispersion is slowly added. The cationic silica sols and their
amounts are recorded in the following Table 1.
TABLE 1
Brookfield Viscosity
(cps)
Ex. silica sol % amountlAs made 4 weeks
1 sol #12 9.0 5 6
2 sol #1 36 83 55
3 sol #23 9.0 10 12
~Amount of sol based on the weight of the ketene dimer size.
7Cationic silica dispersion available from Nalco Chemical under the
name NALCO*-lSJ612.
3Cationic silica dispersion ayailable from E.I. du Pont de Nemours
& Co. under the name LUDOX*CL.
* Denotes Trade Mark
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